The present invention relates to a speed change control apparatus for a vehicular automatic transmission and a troubleshooting method for operating a condition detecting device. More particularly, it relates to an apparatus for speed change control upon failure of a sensor and a troubleshooting method for troubleshooting various sensors, in a speed change control apparatus for setting an optimum transmission stage by fuzzy inference in accordance with operation information from the various sensors.
In a conventional vehicular automatic transmission, shift patterns are prestored in accordance with the throttle opening (engine load) and the velocity of a vehicle, and the transmission stage is set in accordance with the detected throttle opening and vehicle velocity by using the shift patterns, whereby a transmission gear shift is made automatically. According to this conventional automatic speed change control method (non-fuzzy speed change control method), the transmission gear shift can be carried out without any substantial problems when the vehicle is running on a level road, such as one in an urban district, and a speed change can be smoothly made without a shock. Among roads between mountains, however, there are straight ascending roads, winding ascending roads which bend frequently, descending slopes which require positive engine braking, and long gentle downward slopes. Some drivers may suddenly accelerate the vehicle on a downward slope and apply the brakes hard immediately before approaching a corner. While the vehicle is running between the mountains in this manner, it is rather difficult to select an optimum transmission stage for the vehicle operating conditions, driver's intention, road conditions, etc. Accordingly, there is a demand for an arrangement which ensures simple operation, higher vehicle mobility, and better driving feeling for vehicle drives between mountains.
To meet this demand, speed change control methods have been proposed in which the optimum transmission stage corresponding to the aforesaid vehicle operating conditions and the like is selected by executing the so-called fuzzy control. These methods are described, for example, in Published Unexamined Japanese Patent Applications Nos. 63-246546 and 02-3738. According to these conventional speed change control methods (fuzzy speed change control methods), the optimum transmission stage is set by estimating all shift positions for drives in urban districts or between mountains by fuzzy inference. Thus, those conventional speed change control methods based on the fuzzy control are subject to a drawback, namely that many rules are required and membership functions are complicated. Further, their practical application requires use of a large-capacity computer. According to these methods which require many rules and complicated membership functions, tuning is difficult. Therefore, it is also difficult to adapt the application to various kinds of vehicles.
If the speed change control methods based on the fuzzy control are newly adopted, furthermore, drivers who are accustomed to driving vehicles on ordinary level roads, such as ones in urban districts, may have an uneasy feeling as a transmission gear shift is caused by a minor change of the operating conditions, such as clearing a small bump, a slight additional press on the accelerator pedal, etc., which conventionally do not cause a gear shift.
To cope with this, an alternative speed change control method has been proposed in which the optimum transmission stage is selected by fuzzy inference with respect to winding roads between mountains or ascending roads, and the optimum transmission stage is selected from previously set shift patterns in accordance with the vehicle velocity and throttle value opening when the vehicle is running on level roads in urban districts and the like. According to this speed change control method, fine speed change control can be effected depending on the various conditions of the roads between mountains, driver's intentions, etc. without requiring use of any large-capacity computer.
In a fuzzy speed change control mode for setting the optimum transmission stage by the aforesaid fuzzy inference, various sensors must be used to obtain various kinds of information on the engine operation, vehicle conditions, road conditions, driver's intention, etc. If any of these sensors utilized in the fuzzy inference is in trouble, the optimum transmission stage may be diagnosed incorrectly from abnormal data from this broken sensor. During a steady-state drive (constant-speed drive) on a level road, for example, therefore, a downward gear shift may possibly be executed suddenly to cause engine braking, thereby making the driver feel uncomfortable or uneasy.